2D painting from A to Z

This tutorial by David Revoy is really interesting. It sometimes gets a bit dense as the original was in french, but it's worth the effort. He talks about Painter, Photoshop, The Gimp, Daz studio and Artweaver. The last three are all freeware and can replace the others if you're willing to learn them.
The Gimp is open source and similar to Photoshop.It can be a bit tricky to learn,but some people love it.
Daz studio can be used intead of Poser. You can import Poser figures and models into Daz and also other freeware figures such as Apollo Maximus.
Artweaver is like a cross between Photoshop and a stripped down version of Painter.